This spring Wendy Chapman, a professor at the University of California at San Diego's medical school, got a plastic device the size of a sponge from her colleagues in the computer science department. The experimental device was designed to regularly sample the air for ozone, nitrogen dioxide and carbon monoxide, the most common pollutants from car and truck traffic.
For four weeks, Chapman carried it with her all day, occasionally checking her smartphone to see its readings.
Chapman's monitor was part of a system called CitiSense that UC San Diego computer scientists are testing. The CitiSense developers hope that a system of monitors carried by commuters like Chapman someday will give people and city agencies much more detailed data about air pollution than what's available today from air quality monitoring stations.
"We want to get more data and better data, which we can provide to the public," the monitors' lead developer, William Griswold, said in a statement. "We are making the invisible visible."
CitiSense consists of three parts. There are the air pollution monitors, which have Velcro straps so carriers can secure them to their purses, backpacks or bike frames. There's an associated Android app that tells carriers their current level of exposure and where that level falls within U.S. Environmental Protection Agency guidelines. The app also maps the carriers' commute, so that at the end of the day they can see their varying air pollution exposure in different parts of town. Lastly, there is a central server. CitiSense samplers send their data back to the server, which is able to analyze larger trends.
San Diego County, which covers 4,200 square miles, has 10 air quality monitoring stations, as mandated by the EPA. The stations provide forecasts of air quality that are specific to different cities, but they aren't able to detect street-by-street differences. Yet pollution levels may change between locations just a few yards apart.
In the future, if the monitors become more widespread, they could help researchers perform more-precise studies about how air pollution exposure affects people's health, Griswold and his colleagues wrote in a paper they presented in October at a conference about mobile devices for health. Previous studies have linked air pollution to increased risk for lung and heart diseases.
CitiSense might help city dwellers even more directly. Pedestrians and bikers could use the monitors' data to choose less polluted routes. CitiSense researchers noticed that quieter roads often had much less polluted air than a busier street just a block away.
Chapman noticed her pollution exposure varied along her bike ride between UCSD and home. She also noticed she was exposed to less pollution when she drove than when she biked.
"The people who are doing the most to reduce emissions, by biking or taking the bus, were the people who experienced the highest levels of exposure to pollutants," Griswold said.
Griswold and his colleagues still have plenty of engineering to do before their monitors are ready for widespread use. If researchers want to use CitiSense data for formal studies about air pollution and health, they'll need to calibrate the CitiSense monitors regularly, which means a lab visit for monitor carriers. The CitiSense developers say they want to find ways to reduce the number of such visits. The developers also want to find ways to automatically detect and ignore flawed pollution readings, such as readings taken when the monitor's holes were covered.